obama in romney's mock debate sessions. with the two candidates off the trail tuesday, their number two men picked up the slack. campaigning in north carolina vice president biden drew some attention with these comments, discussing the gop ticket's tax plan. >> how they can justify raising taxes on the middle class that's been buried the last four years. >> reporter: the romney campaign pounced on the word buried. campaigning in iowa, paul ryan fired back. >> vice president biden just today said that the middle class over the last four years has been, quote, buried. we agree. that means we need to stop digging by electing mitt romney the next president of the united states. >> reporter: later, the vice president did some damage control, clarifying his remarks. >> the middle class was buried by the policies of romney and ryan supported. >> reporter: 24 hours before the start time of tonight's debate late tuesday, conservatives began circulating a 2007 speech by then candidate obama speaking to an african-american audience ab